Chemistry pt. 7: Valence electrons and ionic compounds

 When we are talking about a group, we are talking about a vertical column. 

Even if a column of elements has different atomic numbers, what matters is its valence elections, meaning they have similar properties, valence electrons are reactive, and elements with similar valence electrons will have similar properties, and when an element has the same amount of valence electrons they are put into a group.
What a "Full outer shell". In chemistry, a full outer shell is when you have 8 electrons, but the only rule here is that the first shell gets full after 2 valence electrons.

Helium, even though it only has 2 elections. It is still a very stable element.

For example, group 18 (vertical column 18), or the "Noble gasses", while the Halogens (group 17) has only 7 valence elections, as they are 1 election away from the noble gasses. These Halogens like to attract electrons, to form a negative ion or an anion, one example is Florine or a -1 Florine anion, -1 Chlorine, or a Chlorine anion, a -1 Iodine. 

If you go to group 16, the Oxygen group, you will find that these elements have 6 valence electrons, so instead of losing 6 elections to become stable, they instead do their best to attract other elections to have 8 valence elections, you might see Oxygen as an Oxide anion (-2 Oxygen), Sulfur as a Sulfuer anion or a -1 Sulfide anion.

The ones on the left most, or group 1 are the Alkali metals, it instead easier to lose one election instead of gaining 7 elections. These Alkali metals want to give away electrons to become stable, so you would often see a Sodium ion with a +1 charge, or a Lithium-ion with a +1 charge. 

Let's go back to Helium, if it wanted to add an electron it would become a Hydrogen atom.